Specifically the ones that measure your temperature as opposed to the weather ones. I know about the mercury but is that in the ones you use for your temperature? And how to the touchless ones work?
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Mercury thermometers work because mercury is a liquid that expands by a very precisely known amount for a given change in temperature (called the coefficient of expansion). Mercury has a very large coefficient of expansion which means its volume increases by a *relatively* large amount for every degree Celsius the temperature increases (and shrinks by an equal amount when the temperature falls).
The bulb at the bottom of the thermometer absorbs some heat from your body, expands and pushes the column of mercury up the tube so you can read it. You could use another liquid like alcohol or water but they have much lower coefficients of expansion which means they would have to use much longer tubes to be equally sensitive.
Wireless thermometers read infrared (heat) radiation coming off an object – like your forehead or a piece of meat on the barbecue. The infrared radiation is focused on an electrical component called a thermopile which creates a small electrical current – the greater the heat, the greater the current. This can be measured and used to generate a display telling you the temperature.
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